The invention relates to a DFB laser diode structure having complex optical grating coupling.
A DFB laser diode structure of this type is known from IEEE Photonics Technology Letters, Vol. 4, July 1992, pages 692-695 or from EP-A-0 507 956.
German reference DE 41 24 872 A1 or B. Borchert et al., Electronics Letters, Vol. 29 (1993), pages 210-211 discloses a DFB laser diode structure that comprises all features of a laser diode structure of the species initially cited, except for the features that the layer of the index material and the layer of the absorption semiconductor material are respectively composed of volumetric material and both the layer of the volumetric index material as well as the layer of the volumetric absorption semiconductor material are located between the one cladding layer and the relief surface in the projections of the grating.
Given this known structure, the layer of the index semiconductor material is present in the defined forward projections of the optical grating, but the layer of the absorption semiconductor material is located only in the defined backward projections of this grating.
These forward projections and backward projections are constructed with, for example, a triangular profile. In this case, the layer made from the absorption semiconductor material which is required for the complex grating coupling should be constructed only at the vertices of the triangular backward projections of the holographically produced grating. Consequently, the effect of the complex coupling depends decisively on how reproducibly the grating shape of the grating, which forms a Bragg grating, can be produced. Fluctuations in the grating shape, which can occur owing to unavoidable fluctuations in the technical process parameters during the production of the grating, therefore have a particularly strong effect in the case of this form of realization of the complex coupling on the intensity of the complex coupling and thus on the spectral characteristics of the DFB laser diode structure.